In order to recover natural resources from subterranean formations it is often necessary to perform tasks related to exploration, monitoring, maintenance and construction in remote locations that are either difficult or impractical for personnel to reach directly. For example, boreholes may be drilled tens of thousands of meters into the earth, and in the case of offshore drilling; the borehole may be thousands of meters under water. One of the technical challenges to performing tasks in such remote locations is providing power to equipment. It is known to power downhole and undersea equipment via stored energy or wireline connection to the surface. However, both of these techniques have disadvantages. For example, a wireline connection to the surface limits that distance at which the equipment can operate relative to the energy source, and may require a relatively significant portion of the limited volume of a borehole. Using stored energy avoids some of the disadvantages of a wireline connection to the surface, but relatively little energy can be stored in comparison to requirements because of size limitations. For example, the available volume in a borehole environment is small. Further, both wireline connections to the surface and stored energy techniques require the presence of operators, e.g., a surface vessel to either provide the wireline energy or recharge the energy storage means.
Various techniques associated with energy production are known. Vibration energy harvesting can be accomplished by developing relative motion, and hence energy, between a vibrating structure and a reaction mass coupled to the structure. Vibration energy harvesting involves the creation of some physical structure that can couple in kinetic energy from vibrations and convert the kinetic energy into storable electric energy. Most harvesters are modeled as single degree-of-freedom second-order spring-mass-damper systems as shown in FIG. 1 and first described by Williams et al., “Analysis of a micro-electric generator for Microsystems,” Sens. Actuators A, Phys., vol. 52, no. 1-3, pp. 8-11, 1996.
Due to the growing demand of autonomous sensors that function without the need for human intervention, interest in this topic has grown rapidly in recent years.